There have been many techniques in the past for displaying the residual capacity of a power supply in a rechargeable electronic apparatus, including in an electrical-generating electronic watch.
For example, in the Japanese Examined Utility Model Publication (KOKOKU) No. 54-29709, there is disclosure of technology that samples a battery voltage, A/D converts the battery voltage from the output of that sampling, and digitally displays the value thereof.
The prior art will be described below, with reference made to relevant drawings. FIG. 12 is a circuit block diagram of a electrical-generating electronic watch, which is an example of a rechargeable electronic apparatus in the past.
In FIG. 12, the reference numeral 1 denotes an overall control circuit, which outputs a sampling signal P1 that controls a voltage detection circuit 2 to be described later and a display control signal P6 that controls a display means 6; 2 is a voltage detection circuit that detects the voltage of an electrical storage means 70 to be described later and which outputs a full-charge detection signal P20; and 3 is an electrical generating means, which in this case is a solar cell.
The reference numeral 4 denotes an overcharging prevention means, which is operated by a signal from the voltage detection circuit 2; 5 is a reverse-flow prevention means; and 6 is a display means which displays the time and the like. The reference numeral 70 is a storage means which stores electrical power that is generated by the electrical generating means 3.
Next, the operation of an electrical-generating electronic watch of the past will be described.
The overall control circuit 1 includes a watch circuit (not shown in the drawing), and outputs time information to the display means. The display means 6 receives that information, and indicates the time and the like on an LCD or by means of indicating hands.
The overall control means 1 also outputs the sampling signal P1 to a charging voltage detection means 20 every hour, for example. By means of this sampling signal P1, the overcharging voltage detection means 20 measures the voltage value of the storage means 70, and if the voltage value exceeds a prescribed voltage (for example 2.6 V), the full-charge detection signal P20 is output.
The overcharging prevention means 4 receives this full-charge detection signal 20 in response to which it turns on, thereby closing a switch, the result of which being that the electrical generating means 3 is shorted, so that electromotive power is not supplied to the electrical storage means 70.
Therefore, it is possible to prevent unnecessary overcharging. Additionally, the full-charge detection signal P20 is also output to the overall control circuit 1, which results in the overall control circuit 1 outputting the display control signal P6. At the display means 6, this display control signal P6 is received, and notification is made that the full-charge condition has been reached.
Recently, titanium-lithium ion secondary cells (hereinafter abbreviated as TL cells), which are large-capacity secondary cells, have come into use as a power source for electrical-generating electronic watches such as described above. This type of TL cell has a significantly greater capacity than even the large-capacitance capacitors used in the past, and as a result there has been a great increase in watch operating time of several months from the full charge condition.
However, a TL cell has charge-discharge characteristics such as shown in FIG. 13, so that it is difficult to gain a grasp of the stored electrical charge by merely measuring the battery voltage such as done in the past. Thus, in an electronic watch that makes use of this type of TL cell, it was not possible to obtain a notification of the so-called full-charge condition, in which operation is possible without any electrical power at all.
There are many known methods of detecting the residual capacity in an electrical storage means and indicating the results thereof.
For example, in the Japanese Unexamined Patent Publication (KOKAI) No. 54-53328, there is language with regard to a method of measuring the residual capacity in a silver battery, the specific method therefor being that of predicting the change in the internal resistance of the silver battery, connecting a load resistance that is equivalent to the predicted internal resistance and measuring the voltage as a means of measuring the residual capacity of the silver battery.
This known technology, however, is strictly with regard to silver batteries, and belongs in a different technology category than that of the power source for a rechargeable electronic apparatus such as in the present invention. For this reason, it is difficult to apply the above-noted prior art as is to the present invention.
In the Japanese Examined Patent Publication (KOKOKU) No. 53-16098, there is disclosure of technology for determining the residual capacity of a storage battery by means of the open-circuit voltage immediately after completion of discharging.
The basic technological concept therein is that of opening the battery after the completion of discharging, however, and in an electronic apparatus such as an electronic watch, which is the target device of the present invention, it is not possible to place the power source in a completely open condition. That is, the present invention only cuts off the path between the electrical generating/charging device and the power source, so that the above-noted prior art cannot be applied thereto.